symtab init_symbols: Condense malloc checks. Fix bad argument check.
symtab init_symbols: Condense malloc checks. Fix bad argument check.

args is set to NULL if there are 0 args for a callable. The previous check
assumed that @main would be the only builtin callable that would have 0 args.

It's unlikely that another builtin will take 0 arguments, but at least there
won't be a crash if that ever happens.

boardwalk/lily,crasm/lily,crasm/lily,crasm/lily,boardwalk/lily